What is the district's policy on acceleration? Get it in writing.
What is the state's law about acceleration? Get that too.
Also, what provision is made in your state for partial homeschooling?
Those will tell you what your options are. If what the district is doing is against state law or its own policy, you have recourse to those. If not, and if this is important enough to you and your child, you may need to look for alternative school options.
It may be possible for you to register as homeschooling in math, and use a curriculum that lets him fly at his own pace.
It may be possible to look at other local schools or districts and see if there's a better option out there.
You may want to find an educational advocate to help you make the case.
Some districts require their own testing for acceleration, and often the requirements are so severe as to be ridiculous. Some really do let the child move ahead without much fuss.
